1. Field of the Invention
The present invention relates to an image display apparatus that can execute displaying and erasing operations of images repeatedly by moving display particles in an electric field.
2. Description of Related Art
Conventionally, an image display apparatus that displays images by moving display particles in a gaseous phase has been known. The image display apparatus has a structure in which display particles in a powder state are sealed between two substrates at least one of which is transparent, and by generating an electric field between the substrates, the display particles are moved and adhered to one of the substrates so that an image is displayed. Upon driving such an image display apparatus, a voltage is applied between the substrates to generate an electric field, and the display particles are moved along the electric field direction so that by selecting the electric field direction on demand, the displaying and erasing operations of images can be executed repeatedly.
However, once the display particles are adhered to the substrate, the display particles become unmovable in the adhered state to the substrate since the display particles have a comparatively high adhesive force, resulting in a problem that the contrast between an image portion and a non-image portion deteriorates.
In order to reduce the adhesive force between the display particles and the substrate, display particles, formed by coating the surface of each of base particles containing a binder resin and a colorant with inorganic fine particles such as hydrophobic silica or hydrophobic titania, by using a dry mixing method by a Henschel mixer or the like, have been known (Japanese Patent-Application Laid-Open No. 2004-29699). However, since the dry mixing method fails to completely cover the surface of each base particle, the adhesive force suppressing effect by the fine particles is not sufficiently exerted. For this reason, after repetitive driving operations, the contrast between the image portion and the non-image portion is lowered.
The present inventors have found a technique in which a metal oxide layer is formed on the surface of each of base particles by using a wet synthesizing method and an organic layer is further formed thereon so that the contrast durability can be improved. In such a technique, however, although the technique provides improving effects of the contrast durability under a normal temperature-normal pressure environment, in a case of repetitive driving operations under a low temperature-low humidity environment, the absolute value of the quantity of charge of each of the display particles increases, resulting in degradation of the contrast.
It is an object of the present invention to provide an image display apparatus that can sufficiently prevent the degradation of contrast at the time of repetitive driving operations for a long period of time, even under a low temperature-low humidity environment.